Datasheet Content
Technical Instructions
Document No. 155-753
SKP55 U..
July 9, 2014
SKP Series
SKP55 U.. Air/Gas Ratio Controlling Actuators
With Safety Shutoff Function
For Use with Gas Valves VG
Description SKP55 pressure regulating electro-hydraulic actuators combine with VG series gas
valves to provide slow opening, fast closing safety shut-off and air/gas ratio control for
industrial and commercial burner applications.
The SKP55 actuator controls the pressure difference across a restriction in the gas
supply line as a function of the pressure difference across a restriction in the air supply
duct so that the air to gas ratio remains constant irrespective of air volume changes.
There is no need for an upstream constant pressure regulator when using an SKP55
actuator within the applicable pressure range of the VG valve body.
Since a single valve performs three functions: safety shut-off, constant pressure
regulation, and air/gas ratio control, fewer components and fittings are required to
assemble a gas train. This significantly reduces both the size and the weight of the gas
train. The total pressure drop across the gas train arrangement is reduced, allowing for
the use of smaller diameter gas trains in most applications.
The modular design allows the SKP55 actuator to be used in combination with all
VG series gas valves from 1/2-inch to 6-inch in size. The actuator is easily mounted
on the square flange of any VG valve with four bolts. No gaskets or seals are
required when mounting the actuator. A visible position indicator on the front of the
actuator displays the entire stroke of the valve. A light indicates when the actuator is
powered.
Siemens Building Technologies, Inc.
Technical Instructions SKP55 U.. Air/Gas Ratio Controlling Actuators
Document No. 155-753
July 9, 2014
Features • UL listed, FM approved, CSA certified for USA and Canada, and ISO 9001 certified;
European, Australian and Japanese approved versions available.
• Safety shut-off function, pressure regulating function and air/gas ratio control in one
compact unit.
• Proof Of Closure with Over Travel (POC) versions.
• Simplifies commissioning and reduces start-up time for:
o Recuperative burners with combustion air preheating.
o Burners with continuously variable air or gas nozzle openings in the burner
head.
o Burners where either the air or gas pressure is not representative of the actual
flow.
o Burners with negative combustion air pressure levels.
• Maintains air/gas ratio when the airflow is disrupted.
• Automatic compensation for combustion chamber back pressure fluctuations.
• No mechanical wear or play that causes drifting.
• Visual stroke position indicator.
• Light indicating "power on".
• Optional auxiliary switch available.
• )
Excellent tracking characteristic.
• Low, 13.5 VA power consumption.
Application SKP55 series actuators may be combined with 1/2-inch to 6-inch VG series gas valve
bodies. VG series gas valves are ordered as separate items (See VG U.. Technical
Instructions P/N 155-512P25).
Product Numbers
Table 1.
Product Number Operating Proof of Closure Auxiliary Switch Type of Switch
Voltage Switch
SKP55.011U1 x – SPDT
SKP55.012U1 110 to 120 Vac x x SPDT SPDT
SKP55.013U1 – –
SKP55.012U2 x x SPDT SPDT
220 to 240 Vac
SKP55.013U2 – –
Accessories
Table 2.
Product Number Description
AGA66 Sealing gasket to provide NEMA 3, 3R, and 4 protection (for VGG/D valves)
Page 2 Siemens Building Technologies, Inc.
SKP55 U.. Air/Gas Ratio Controlling Actuators Technical Instructions
Document No. 155-753
July 9, 2014
Specifications As safety shut-off valve UL/429, FM/7400, ANSI Z21.21/CSA6.5 C/I
in combination with VG U.. series gas
valves
Agency approvals
As a pressure regulator ANSI Z21.18/CSA6.3
Power supply Operating voltage 110 to 120 Vac + 10% to 15%
220 to 240 Vac + 10% to 15%
Operating frequency 50 to 60 Hz + 6%
Power consumption 13.5 VA
Duty cycle 100%
Operating Ambient operating temperature 5°F to 140°F (-15°C to 60°C)
environment Mounting position Optional, with diaphragms in vertical
position except upside down
Maximum inlet gas pressure Same as VG valve
Physical Weight 4.2 lb (1.90 kg)
characteristics Enclosure NEMA 1, 2, 5 and 12 for indoor use
NEMA 3, 3R, and 4 with sealing gasket
AGA66 (only for VGG/F/D valves)
Dimensions See Figure 4
Specification for valves See gas valve Technical Instructions
P/N 155-512P25
Connections Conduit connection Two 1/2-inch NPSM threaded knock-outs
Electrical connection Spring loaded terminals for 14 AWG wires
Gas/air pressure connections 1/4” NPT
Operating Output force ) 100 lb (450 N)
characteristics Maximum stroke 1 inch (26 mm)
Opening time for maximum stroke Varies with valve size, 14 seconds for max.
stroke
Closing time < 0.8 seconds
Reference input signal Combustion air pressure difference
Control signal
Control characteristic Integral action
Operation/installation Differential pressure ratio 1:1
Permissible pressure differences
during operation for accurate control Gas: Minimum 0.1" w.c.
Gas: maximum 80" w.c.
Air: minimum 0.1" w.c.
Air: maximum 80" w.c.
Minimum time required for high to low
fire load changes Approx. 5 seconds
Permissible leakage test pressure 20 psi
Permissible leakage test vacuum 3 psi
Minimum diameter of impulse pipe 1/4” inside diameter
Low fire bias range -0.4 to 0.4" w.c.
Minimum distance of
impulse pipe connections 3 pipe diameters before and 5 pipe
diameters after any valve, damper, elbow,
coupling, or flow disruption
Auxiliary features Proof of closure switch Non-adjustable
Capacity of auxiliary switch 6 (3) A, 250 Vac
Setting range of auxiliary switch 40% to 100% of stroke
Siemens Building Technologies, Inc. Page 3
Technical Instructions SKP55 U.. Air/Gas Ratio Controlling Actuators
Document No. 155-753
July 9, 2014
Operation The electro-hydraulic actuator consists of a cylinder filled with oil, and a piston containing
an electric oscillating pump and a relief system. When power is supplied to the actuator
(See Figure 1)
the relief system closes, and the pump moves oil from the reservoir into the pressure
chamber. This action causes the piston to move downward in the cylinder, opening the
Safety Shut-off gas valve. When power to the pump is interrupted, the relief system opens and the gas
Function valve closes in less than 0.8 seconds.
A pointer, visible through the transparent portion of the terminal box cover, indicates the
entire stroke range of the actuator. A light, which is visible through the lower left…
